


Big brother does it better

by Thatthingrightthere



Category: Osomatsu-san
Genre: Cheating, Creampie, F/M, I’m sorry Karamatsu, Osomatsu/Reader - Freeform, Relationship ruined, Smut, i should be studying
Language: English
Status: Completed
Published: 2018-05-16
Updated: 2018-05-16
Packaged: 2019-05-08 00:08:25
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,339
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14682351
Author URL: https://archiveofourown.org/users/Thatthingrightthere/pseuds/Thatthingrightthere
Summary: You aren’t happy with the sex you’re having with your boyfriend.So you fuck his older brother.





	Big brother does it better

**Author's Note:**

> wow i should be revising for my GCSE’s that are currently happening but no i will write porn about fictional characters 
> 
>  
> 
> probably super OOC too lmao

Your relationship with Karamatsu was almost perfect. Despite his painful personality, he was incredibly sweet. 

He’d always welcome you home with a love filled kiss before he goes back to setting fire to the house in an attempt to cook dinner. 

He often got you gifts of roses and chocolates because “You are so wonderful, I don’t feel my heart is enough!”.

His parents were happy with your relationship as well. They just about begged you to marry him when they found out but the two of you had decided to take it slow. 

Everything was just about perfect. Apart from one thing.

The sex.

Karamatsu’s sweetness even extended in to your more intimate moments, much to your dismay. You wanted something more exciting than boring, slow missionary sex. You had asked but he simply couldn’t. This left you incredibly unsatisfied. And was probably the reason you ended up cheating on him with his older brother.

——————

You’d ended up hanging around your loving boyfriend’s house because he’d been too busy trying to get a job. Too bad that was exactly what he was doing at that moment. You’d planned a romantic date and everything. But you were proud of him for trying. He’d been trying ever since the two of you had started dating because he “wanted to be the man and support his honey”. Now you were just awkwardly sat in the living room, on the floor, waiting for him to get back. You weren’t the only one though. Sitting across from you on the floor was Karamatsu’s older brother, Osomatsu, who’s been eyeing you for the past half an hour. 

“Do you need anything? If not please stop staring at me...”

He blinked a couple times before answering you with a shit eating grin.

“You.”

His blunt response left you confused and speechless, allowing Osomatsu to slowly crawl and sit directly in front of you. You only came to your senses when he’d placed a hand on your thigh. Then you promptly smacked his hand away. But why did you feel so hot?

“Osomatsu, I can’t believe you’d stoop so low as to hit on your brother’s girlfriend! The hell’s wrong with you?”

“You’re pretty hot and I’m still a virgin. No one needs to know...”

You couldn’t believe this. He wanted you to cheat on your boyfriend and his brother, in the living room where anyone could come in! The idea was idiotic. To the point where you think it may be a test to show your loyalty to Karamatsu but the small tent in Osomatsu’s trousers was telling you otherwise. Was he just sat there thinking about the two of you fucking? You wouldn’t be surprised. What did surprise you was the slight wetness in your panties over the thought of doing something so risky.

“No, if Karamatsu found out he’d be distraught. He’s already got esteem issues because of you and your brothers and I don’t wanna think of how he’d react to me cheating on him.”

“So lets do this quickly then!”

Both of his hands were now on your shoulders as he pulled you to in to a desperate and rough kiss that greatly contrasted the gentle and loving kisses you shared with Karamatsu. Your teeth bumped together every so often and this was clearly his first time kissing someone, but it felt oddly good. To the point you even kissed back a little until you realised you were shoving your tongue in you boyfriend’s older brother’s mouth. You then promptly shoved him away before wiping your mouth of stray saliva.

“What the fuck are you doing, you pervy little shit?!”

“What are you doing? You kissed back, you want this don’t you?”

You couldn’t answer. You wanted to. You needed to say no. But you just couldn’t. The word got stuck in your throat as possibilities flooded your brain. If you got away with this you may have the best orgasm of your life. Or maybe just an orgasm, you haven’t cum in months. Probably not, this guy’s a virgin. But the chance of getting caught and doing it in the living room while not knowing when anyone is getting back was making you wet. If you got caught you’d ruin your longest relationship. The pros and cons seemed to be completely balanced. You had no answer. So Osomatsu made one for you.

His lips pressed against yours softly this time as his fingers lightly brushed against your thighs, leaving goosebumps in their wake. You busied yourself by grasping the man in front of you by the hair and pulling him closer for a deeper kiss. His tongue snuck in to your mouth as the two of you began to get more heated. He pushed a hand between your legs to feel you through your moist panties while his other palmed his erection through his jeans. You broke the kiss to whimper quietly. You’d only just started yet you were desperate to have him inside of you. Osomatsu seemed to feel your lust as he paused his movements to pull you on to his lap and grind his clothed cock against your aching pussy. You helped by rocking your hips causing the two of you to groan from the addicting friction. He began to bite and leave open mouthed kisses up and down your throat. Your hips bucked at the feeling. You couldn’t take it anymore. You needed his dick deep inside you. You wanted to feel him rub your inner walls as he cried out your name. You were now determined.

You lifted yourself up slightly so you could undo his jeans and pull his boxers down slightly until his solid boner was freed from its tight prison. You jerked him off a little bit to get a little bit of revenge on him for turning you on like this before you pulled your underwear aside and sat yourself on his precum covered cock. He moaned louder than you expected but you figured it was probably because you were taking his virginity. You were also whining too. His member was slightly thicker than your boyfriend’s but the extra thickness made so much difference. You began to fondle your clit with one hand and pull Osomatsu’s hair with the other. Between his groans and pants he spoke much to your surprise yet pleasure.

“Oh fuck... You’re so tight and warm around my dick... Shit you like that don’t you? I do it way- nng- better than Karamatsu... I am the oldest after- ah- all”

His dirty talk fuelled the fire in your stomach that caused your lower half to tingle. You were getting close. Osomatsu had apparently had enough of your position though because he suddenly leant forward and threw you on the floor so he could take control. And it was the best decision he’d made. He was now even deeper inside of you. He drooled as he continued to describe how you feel around him and brag how he was making you feel better than Karamatsu has probably ever done. You wrapped your legs around his waist to get even closer to the man pounding your wet hole though it probably wasn’t possible. His balls slapped against your ass which added to the obscene noises the two of you were making. He was ramming you so hard and deep. This was what you’d been missing in your relationship. You were finally going to cum. Both of you were.

“Ah shit! I’m going to cum! I’m going to cum inside!” 

You would’ve probably stopped him if you weren’t yelling his name and grabbing his red hoodie while you came all over his swollen dick. You only realised when your insides suddenly felt like they were burning as Osomatsu emptied himself inside of you. Then you fully realised what you had done. 

You had let your boyfriend’s older brother cum inside of you while he was out looking for a job to support you and your life together.

You fucked up.

**Author's Note:**

> How would you guys feel if this became an angsty, multiple part story rather than just smut?


End file.
